Making a commitment to live together and build a future is something many young people choose to do when they find the right one, but few of them realize that people mature at different rates. They might be perfect for each other when they are both young, but the need to mature and deal with reality can take a toll on the relationship over time. If only one of them becomes a truly responsible adult, there will be issues arising on a regular basis. Living with an immature partner can make people decide a relationship is not working.
The partner who chooses to be immature is taking advantage of the person they are supposed to be supporting, and their lack of discipline can make life difficult for both of them. They seldom see this angle of it because they place fault on others for their own behavior, and it can eventually ensure they will lose their partner.